Mapping: Fixed unconditional use of MPI routines.
Mapping: Fixed unconditional use of MPI routines.

When using MPI routines without MPI init, an error is thrown.
However, MPI init is only used with PETSc routines.
As a quick workaround, only use MPI routines when PETSc is used.

viennashe/viennashe-dev,viennashe/viennashe-dev